1. Field of the Invention
This invention relates to a radiation shield for use with a manned spacecraft.
2. Description of the Prior Art
In support of human exploration of space, manned spacecraft must be designed to provide a habitable environment for people in an extraterrestrial setting. A major area of concern in the design and development of such vessels is exposure to dangerous levels of radiation that exist in space.
Space radiation ranges from electromagnetic waves including gamma rays to elementary particles such as electrons, protons, and neutrons to heavier particles including alpha particles. The levels of radiation that exist in space can cause illness, including cancer, and even death to humans. Also, this level of radiation can interfere with the operation of electronic instrumentation vital to the operation of a spacecraft.
Compounding this problem is the fact that many manned space missions are of a long duration. This increased expose to the radiation increases the risk of injury, since damage due to radiation exposure is cumulative. For long interplanetary trips, this risk increases significantly.
Such risks are not manifest on Earth due to the magnetic field, atmosphere, and rotation that limits direct exposure to radiation emitted by the Sun. These factors reduces harmful space radiation on the surface of the planet. Spacecraft, however, must rely upon different types of radiation shielding techniques.
There are a variety of radioactive shielding materials. One such well-known material is Lead. While Lead is effective at shielding against radiation it has drawbacks in a space environment. Particularly with the high cost of placing a payload into space, Lead is not an economically effective solution due to Lead's mass.
Also, Lead can fragment into potentially dangerous secondary particles and reradiate when impacted by high-energy radiation. The characteristic of metals, like Lead, to re-radiate when impacted with high-energy radiation is also known as the Bremsstrahlung effect. This secondary source of radiation is not desirable and may also be harmful.
Hydrogen is another good shielding material. Hydrogen does not fragment when impacted by radiation and does not re-radiate like metals. Further, hydrogen can diffuse or break down radiation. A few disadvantages to using Hydrogen are that it is potentially flammable in its gaseous state and, in that state, tends to permeate through many materials.
One solution is the use of water as a radiation shield. Due to the concentration of Hydrogen in water, the water tends to disperse and break down radiation. Also, water is more easily contained and safer than liquid or gaseous Hydrogen.
Even though water is a good choice for shielding against exposure to space radiation, it also has a relatively substantial mass and a spacecraft completely enclosed in a water blanket radiation barrier would not be practical.
While the use of a radiation absorbing material in space applications is important, the deployment of such a material is equally important. In most cases, a shield is set in place before launch. In such cases, the shield cannot be moved once the spacecraft is deployed into space.
Depending upon such factors as the exposure of any portion of the spacecraft to a radiation source, the displacement of equipment and people within the craft, and the duration of the mission, it may not be necessary, or desirable, to have a radiation shield surrounding the entire craft. Also, the shielding required at some locations may vary depending upon the variables mentioned above.
What is needed is a way of incorporating radiation shields in a spacecraft in a manner that allows the crew to position the shields at optimum locations.